Armpit Swelling After COVID-19 Vaccine May Mimic Breast Cancer

Roxanne Nelson, RN, BSN

February 25, 2021

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Axillary adenopathy, or swelling under the armpit, has been reported by women after receiving the Pfizer-BioNTech and Moderna COVID-19 vaccines, but it is also a common symptom for breast cancer.

Hence, clinicians should consider recent COVID-19 vaccination history in the differential diagnosis of patients who present with unilateral axillary adenopathy, according to a new article.

"We noticed an increasing number of patients with swollen lymph nodes on just one side/one underarm who presented for routine screening mammography or ultrasound, and some women who actually felt these swollen nodes," said author Katerina Dodelzon, MD, assistant professor of clinical radiology, Weill Cornell Medicine, New York City.

"Historically, swollen lymph nodes on just one side are relatively rare and are an uncommon occurrence on screening mammography ― seen only 0.02% to 0.04% of the time ― and is a sign that alerts a radiologist to exclude the presence of breast malignancy on that side," she added.

In an article published in Clinical Imaging, Dodelzon and colleagues describe four cases involving women who received a COVID-19 vaccine and then sought breast screening. In describing these cases, the authors sought "to inform the medical community to consider this benign and self-resolving diagnosis in the setting of what can be alarming presentation of unilateral axillary adenopathy."

They hope they will decrease unnecessary biopsies and help reassure patients.

Adenopathy has been reported in association with other vaccines, such as the bacille Calmette-Guérin vaccine, influenza vaccines, and the human papillomavirus vaccine, commented Jessica W. T. Leung, MD, president of the Society of Breast Imaging (SBI).

"It's too early to say if there is something different about the COVID-19 vaccines," said Leung, who is also professor of diagnostic radiology and deputy chair of breast imaging at the University of Texas MD Anderson Cancer Center, Houston, Texas.

"The two vaccines that are currently in use — Pfizer and Moderna — are both mRNA vaccines, and it is unknown if those will give a stronger immune response," she said. "If the Johnson & Johnson and AstraZeneca vaccines do become available, it will be interesting to see if they elicit as strong a response, since they are not mRNA vaccines. At this time, we have no data to say one way or the other."

Leung also noted that these latest vaccine reactions may be getting more attention because "it is COVID-19 related, and everything related to COVID-19 gets more attention.

"It may also be more noticeable because of the large number of people getting vaccinated within a short period of time in an effort to contain the pandemic, and this is not the case with the other vaccines," she said.

New Recommendations From SBI

The SBI recently issued recommendations to clinicians that women who experience axillary adenopathy and who have recently been vaccinated on the same side on which the adenopathy occurs be followed for a few weeks to see whether the lymph nodes return to normal, rather than undergo biopsy.

"Many practices are now routinely inquiring about history of recent vaccination and on which side it was given," Dodelzon said. She emphasized that women should feel empowered to share that history if they are not asked.

"Letting your mammography technologist or breast imager know that you have recently been vaccinated, and on which side, will provide the breast imager more accurate context within which to interpret the results," she said.

In addition, the SBI recommends that, if feasible, women schedule routine screening mammography either before the first dose of the COVID-19 vaccineor 4 to 6 weeks after the second dose to avoid a false positive finding.

"We want to emphasize that screening mammography is very important, and if possible, to schedule it around the vaccine," commented Leung. "But that may not be possible, as most of us don't have a choice when to get the vaccine."

If it is not possible to reschedule either the mammogram or the vaccine, Leung recommends that women inform the facility that they have recently received a COVID-19 vaccine. "Currently, we recommend a follow-up in 4 to 12 weeks," she said. "The swelling could subside sooner, perhaps even within 1 to 2 weeks, but we generally recommend waiting at least 4 weeks to capture the majority of women."

Differences Between the Vaccines?

The frequency with which axillary adenopathy occurs as a side effect differs with the two COVID-19 vaccines, according to reports from the Centers for Disease Control and Prevention (CDC).

For the Moderna vaccine, axillary adenopathy ipsilateral to the vaccination arm was the second most frequently reported local reaction, with 11.6% of recipients aged 18 to 64 years reporting it after the first dose, and 16.0% reporting it after the second. The average duration of this adenopathy was 1 to 2 days.

For the Pfizer-BioNTech COVID-19 vaccine, the CDC notes that reports of adenopathy were imbalanced between the vaccine and placebo groups and concluded that adenopathy was plausibly related to the vaccine.

The average duration of adenopathy was approximately 10 days.

Adenopathy was reported within 2 to 4 days after vaccination for both vaccine groups, the CDC notes.

However, details from the cases reported by Dodelszon and colleagues paint a somewhat different picture. For example, in case 1, the patient self-detected unilateral axillary adenopathy 9 days after receiving the first dose of the Pfizer-BioNTech vaccine. In case 3, the time between receiving the Moderna vaccine and detection of adenopathy was 13 days.

In both of these cases, the time was much longer than the average duration of 1 to 2 days noted by the CDC. The authors suggest that in taking the patient's vaccination history, radiologists understand that the side effect may occur up to several weeks following the COVID-19 vaccination.

In cases 2 and 4, the axillary adenopathy was incidentally noted during mammography, so it is unclear when the onset of this reaction occurred after receiving the COVID-19 vaccine.

The authors and Leung have disclosed no relevant financial relationships.

Clin Imaging. Published online January 18, 2021. Full text

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